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Patented June 29, 1937 PATENT OFFICE PAPER Herbert A. Lubs, Wilmington,Del., and John R. Roberts and Edwin R. Laughlin, Penns Grove, N. J.,assignors to E. I. du Pont de Nemours &

' Company, Wilmington, Del., a corporation of Delaware No Drawing.Application April 16, 1935, Serial No. 16,612

10 1 Claims.

This invention relates to a method for the preparation of an improveddyed paper and more particularly to a process of after treating surfacecolored paper.

Colored paper maybe made by two processes. The color may be added to thepaper before sheet formation by adding the color to the pulp in thebeater. -The more convenient and economical method is, however, thecoloring of the sheet after it has been formed, bydipping orcalendering'. In the dipping process the sheet is dipped directly into adye solution and allowed to drain, or the sheet is passed between rolls,one of which carries a film'of dye solution to'the surface of the paper,and is then passed through squeeze rolls for removing the excess dyesolution from the paper. This latter rolls process is preferred to theprocess inwhich the sheet is passed into the dye solution. In thecalendering process the dyeing is accomplished by placing dy'e boxes onthe calender stack in contact with the calender rolls. In this processdyeing and calendering are accomplished in one operation.

Surface colored paper though much more eco- 5 nomical to produce thanthat formed by the process wherein the coloring matter is added to thepulp before sheet formation, has the disadvantage of producing a color,even when basic or direct dyes are used, which will smudge or crock fromthe surface of the sheet and which is easily affected by contact withwater or a moist object. This ready removal of the color is highlyobjectionable in that the color of the paper itself is affected withspots and streaks and any object coming in contact with the paper in thepresence of water is badly stained.

Various classes of dyes have been used for the coloring of paper. Basicand direct dyes have an appreciable aiiinityfor the cellulose fiberwhile acid dyes have very little affinity for the cellulose, but possessmore satisfactory fastness to light than the basic colors and are moresoluble than the direct colors. 7

Various methods have been suggested to overcome the disadvantage ofsurface colored papers outlined above. Thus, the moist sheet surfacecolored with basic dyes may be-after treated with sulfurized phenoliccompounds. This process is highly effective but is applicable only tothe basic 5 colors which are comparatively fugitive to light. Draves U.S. Patent No. 1,926,614 discloses a process for rendering paper surfacedyed with direct or acid colors non-bleeding by means of an aftertreatment with a diaryl guanidine. Al- 55 though improved results areobtained by this process still further improvement may be realized.

This invention has as an object the preparation of an improved surfacecolored paper. A further object is the preparation of a non-crockingsurface colored paper. A still further object is the preparation of anon-bleeding surface colored paper fast to the action of water. A stillfurther object is the fastness of the dye stuff on surface colored paperafter the paper is after treated. Other objects will appear hereinafter.

These objects are accomplished by the following invention wherein thepaper surface colored with a dye soluble in aqueous solutions andpreferably surface colored with an acid or direct dye is subjected to anafter treatment with an aqueous solution of deacetylated chitin.

Deacetylated chitin is a material whichhas only recently been availableto the art. In copending application of George W. Rigby, Serial No.731,600, filed June 21, 1934, there is disclosed a method for thepreparationof a suitable deacetylated chitin. In this method shrimp,lobster or crab shells, freed from contaminant adherent material, suchas flesh, by treatment with 1% solution of soda ash at the boilingtemperature, then freed from lime salts by treatment with 5%hydrochloric acid followed by a second boiling with 1% soda ashsolution, is deacetylated by treatment with caustic alkali at anelevated temperature for a considerable time, for example, with 40%sodium hydroxide at 110 C. for about four hours. Depending upon theconditions of this alkali treatment the material obtained contains from20%-90% and preferably 70%-90% of its nitrogen in free amino groups,

The viscosity of the solutions made from the v deacetylated chitin ismarkedly influenced by dryingand other treatments to which the materialis exposed. More drastic treatment than that exemplified above resultsin a material of low viscosity. Less drastic treatment than that aboveexemplified results in a material of increased viscosity. A materialobtained by a given treatment may be increased in viscosity by heatingfor a considerable length of time or decreased by the addition ofsuitable deoxidizing agents, such as hydrogen peroxide, to an aqueoussolution of a salt or to a suspension of the solid deacetylated chitin.

The Rigby application mentioned above discloses the preparation ofnumerous soluble salts of this material. The acetate of deacetylatedchitin is preferred because of its ready availability, low cost and easeof use and the volatility of acetic acid, but other acids which formwater soluble salts with deacetylated chitin may also be used.

Having outlined above the general principle and purposes of theinvention and described the unusual material which is used in theprocess of the present invention the following exemplifications of theprocess are given for purposes of illustration but not in limitation.

Example 1 A solution containing gms. per liter of Crocein Scarlet(Colour Index 252) was prepared. Tissue paper was surface dyed byimmersion, drained to remove superfluous dye solution and dried at 200F. The tissue paper which was dyed a heavy red shade was very sensitivetoward moisture. If sprinkled, the color ran badly and moistened paperor cloth-brought into contact with it was badly stained.

The dried dyed tissue paper was immersed in a solution containing 0.78,gm. high viscosity de- The process was applied to calender dyeing byplacing a box upon the calender stack in such a position that the paper,after being coated with a dye solution contained in one box was treatedwith a deacetylated chitin solution contained in a second box. Thus theprocesswas satisfactorily applied to 16' point paperboard by applying 50lbs. Metanil Yellow (Colour Index 138) in 100 gallons water from thetop' box on the calender stack and 15 .lbs. 10 oz. deacetylated chitinin 100 gallons .water from a lower box :on the calender stack after theboard had been colored from the box on the upper roll.

The above examples illustrate the use of two acid dyes. Acid dyes ingeneral may be em ployed in the process of the present invention.Further acid dyes which have been used and which are given inillustration of the wide range of the applicability of the invention are7 Colour Index Fast Acid Blue 2108 Acid Viole u 6:93 Acid Green 6166Pontacyl BlueBlack SX 2146 Orange II 151 Tartrazine '640 A solutioncontaining 10 gms. per liter of -Pontamine Sky Blue 6.BX (ColourIndeX51lB) was used for dip dyeing tissue paper. The dyed paper withoutdrying was immersed in a de-' acetylated chitin solution containing 0.3gm. per liter. The paper was subsequently dried at 200 F. The stabilityof the treated dyed paper was acid and direct dyes. These dyes thereforerepresent a very much more preferred embodiment of the invention.

The concentration of the dye liquor depends on the depth of shadedesired andthe abscrbencyof the paper. It varies from a small fractionof a per cent solution up to a saturated solution, the latter dependingupon the solubility'of the dyestuilf. Dyeing and after-treating may bedone at room temperature or at higher temperatures up to the boil.Drying may be done at any temperature that will not burn the paper.,Best

results were obtained in deep shades by using 21-30 oz. of a 5% solutionof deacetylated chitin as the acetate in 10 gallons of water. Lightshades required less deacetylated chitin and direct colors required lessdeacetylated chitin than acid 7 colors. k

While theexamples show the use of acid and direct colors separately,they-may be usedtogether. Best results were obtained by using the colorfirst and then the deacetylated chitin, the pretreatment 'with .thedeacetylated chitin ,followed by dyeing being less satisfactory. The paper may be dried after dyeing as shown in Example 1 or treated withoutdrying as shown in Example 3.

The drying of the surface colored paper after treating with deacetylatedchitin solution causes a reaction to take place wherein the deacetylatedchitin acetate losesacetic acid with the formation of deacetylatedchitin which is'itself insoluble in water. This "process may beaccelerated by heating which may also cause a further chemical change,in that the deacetylated chitin acetate may react with the loss of waterto form an amide type compound. Treatment with acid anhydrides or acidchlorides also has the same effect. The dried paper containingdeacetylated chitin either as such or as the acetate may also be treatedwith a variety of reagents which react with the carbohydrate aminepolymer and insolubilize the deacetylated chitin. Formaldehyde andglyoxal are examples of such material. I

While the invention has been described in de-- tail in terms ofdeacetylated chitin whichis obtainable from shrimp, crab or lobstershells, which are preferred because of their ready availability, thecomparative ease of preparation of the deacetylated chitin, andthe'convenienceof vits use, the invention is generally applicable to theuse, in the treatment of surface-colored paper to prevent smudging,bleeding and the like, of deacetylated chitin insoluble in water oralkaline media, but solublein aqueous organic acid media. and depositingcoherent films therefrom, i. e, organic acid soluble deacetylatedchitin. In-

stead of shrimp, lobster or crab chitin, chitin derived from the outerinteguments of insects such as locusts, grasshoppers, and the like, maybe used. Deacetylated chitin from vegetable sources such as myceliumfrom fungi such as Aspergillus niger may likewise be employed.

In the claims the phrase surface-colored paper after-impregnated withdeacetylated chitin is used to denote a dyed paper which is impregnatedwith deacetylated chitin after dyeing, i. e., the paper is dyed andthereafterimpregnated.

The above description and examples are intended to be illustrative only.Any modification of or variation therefrom which conforms to the spiritof the invention is intended to be included within the scope of theclaims.

We claim:

1. Process of preparing an improved colored paper which comprisesimmersing paper in a solution of Crocein Scarlet, removing excess dyesolution, drying, immersing in a solution of deacetylated chitin andagain drying.

2. Process of preparing an improved colored paper which comprisesapplying an aqueous solution of a deacetylated chitin acetate to a sheetof paper surface colored with an acid dye.

3. Process of preparing an improved colored paper which comprisesapplying an aqueous solution of a salt of deacetylated chitin to a sheetof paper surface colored with an acid dye.

4. Process of preparingan improved colored paper which comprisesapplying an aqueous so lution of a salt of deacetylated chitin to asheet of paper surface colored with a direct dye.

5. Process of preparing an improved colored paper which comprisesapplying an aqueous solution of a deacetylated chitin acetate to a sheetof paper surface colored with a direct dye.

6. Process of preparing an improved surface colored paper whichcomprises impregnating a surface colored paper with an aqueous solutionof a salt of deacetylated chitin.

7. Process of preparing an improved surface colored paper whichcomprises impregnating a surface colored paper with an aqueous solutionof an acetate of deacetylated chitin.

8. Surface colored paper after-impregnated with deacetylated chitin.

9. Acid dye surface colored paper after-impregnated with deacetylatedchitin.

10. Direct dye surface colored paper after-impregnated with deacetylatedchitin.

HERBERT A. LUBS. JOHN R. ROBERTS. EDWIN R. LAUGHLIN.

